February may be the shortest month of the year, but
its sky is long on mid-winter binocular treasures. We all know many favorite
objects, like the Orion Nebula and the Pleiades. But rather than rehash these,
let's break some unfamiliar ground in the southern sky and enjoy some lesser
known gems that lie within the faint constellation of Puppis, the Poopdeck of
the fabled ship Argo Navis.
Above: Winter star map from Star
by Phil Harrington.
Finder chart for this month's Binocular Universe.
adapted from Touring
Binoculars Atlas (TUBA)
Back in March 2012, this
column surveyed some of what Puppis has to offer, including the striking
open clusters M46, M47, and M93. This month, we return to the scene to visit
some objects to their east.
For those of us in mid-northern latitudes, the targets
this month are going to be a challenge. You'll need a good view to the
south-southwest and get outside right as evening twilight ends. But you are
viewing from south of about 30 degrees north latitude, these objects should all
be fairly easy to identify.
We begin with NGC 2451, a striking, but often ignored,
open cluster. Thirty or so stars are within range of 50-mm binoculars, with the
remainder creating a vague background shimmer. Highlighting the scene is c
Puppis, the cluster's brightest star. This red beacon stands out well amid a
bevy of blue white stellar jewels. With an apparent diameter of 45 arc minutes,
NGC 2451 is too broad to cram into most telescope fields, but it is wonderful
for the wider fields of binoculars.
But hold on there. Is NGC 2451 really an open cluster?
That's how it is listed in Dreyer's NGC, which is based on earlier observations
by John Herschel. Herschel, in turn, had based his observations on even earlier
records by Giovanni Bapista Hodierna. Hodierna is credited with the group's
discovery sometime before the 1654 publication of his catalog of deep-sky
objects. But more recent studies, beginning in the mid-1980s, now cast doubt on
this being an open cluster. A 1994 paper written by German astronomers Siegfried
Roser and Ulrich Bastian and published in Astronomy and Astrophysics provides
good evidence that the stars we see in NGC 2451 are not gravitationally bound to
one another. So, when we look its way, we are not really seeing a true object at
all. Or are we?
That's because Roser and Bastian did uncover some two
dozen stars in the surrounding area that have the same proper motion (that is,
they are moving through space together). They dubbed these as the Puppis Moving
Group, but also emphasized that these do not constitute NGC 2451. The Puppis
Moving Group lies some 600 light years from Earth.
They also suspected that several more distant stars in
the region form a second open cluster lying some 1,300 light years away. Several
sources, both on-line as well as in print, refer to the Puppis Moving Group as
NGC 2451A and the second cluster as NGC 2451B. That's not technically accurate,
however, since this is not the way they were originally recorded in the New
General Catalog. Call it what you will, NGC 2451 is a striking stellar cache
through binoculars. Don't let this part of the sky slip away without catching a
NGC 2477 is found about a degree southeast of NGC 2451
and just north of 4th-magnitude b Puppis. While pale in comparison, it is still
worth a mention. Through 10x50 binoculars, it appears as a starless smudge of
grayish light about the size of the full moon. But increase magnification and
aperture to 15x70s and above, and NGC 2477 will begin to reveal the brightest of
its 160 stars. None shines brighter than 10th magnitude, and so will require
exceptionally clear nights for easy detection. In his book The Caldwell Objects,
author Stephen O'Meara notes that through his 4-inch refractor many of the stars
in NGC 2477 appear to be arranged in several parallel rows that stretch out from
a backbone of other stars. He compares the overall appearance to that of
"an X-ray of the human torso with a spine and a rib cage." Can this
same effect be seen through 80-mm and larger binoculars? Take a look and let me
Continue eastward another 4 degrees for our next
port-of-call, NGC 2546. This is a loosely gathered grouping of some 40 suns
strewn across nearly 3/4 of a degree and ranging in brightness from magnitudes 6
to 11. Through my tripod-mounted 10x50 binoculars, I can see about twenty faint
stars framed by an isosceles triangle of three 7th- and 8th-magnitude suns. The
cluster's brightest star, a 6.5-magnitude blue-white inferno, lies in the
group's southeastern corner.
For this next object, head 8 degrees north-northeast to
a pair of challenging open clusters. NGC 2571 is a collection of about two dozen
9th-magnitude suns. The combined light of this open cluster's stars equals 7th
magnitude. The second, NGC 2567, is even dimmer and smaller. I've never made a
convincing observation of this one through my 10x50s, but have it on my
"16x70 To Do List" for this winter.
Let's head back north for NGC 2539. Unlike the previous
two targets, this open cluster is easy to glimpse through nearly all binoculars.
You'll find it 7 degrees due south of the bright open cluster M48, and 8 degrees
east-northeast of another beauty, M47. The light of the 50 suns within NGC 2539
combines to magnitude 6.5. My 10x50s show an ill defined blotch of light
apparently touching the unrelated 5th-magnitude 19 Puppis. By upping my game to
my 16x70s, I can begin to make out some of the cluster's true stars, which shine
between magnitudes 9 and 11. The two brightest cluster stars are a 9.1-magnitude
red giant and a 9.6-magnitude orange giant. Even larger binoculars may offer
subtle hints of their colors by first slightly defocusing the view.
We've only just scratched the surface of all that Puppis
has to offer. Check the list below for even more tempting targets, as well as a
renegade from nearby Pyxis. Be sure to post your results in this column's
Next month, let's try something a little different, what
is for some a seasonal rite of passage. Until then, remember my stargazing mantra: two eyes are better than
About the Author:
Harrington has written 9 books on astronomy, including Star Ware,
Watch, and his latest, Cosmic Challenge. Visit his
web site, www.philharrington.net,
copyright 2014 by Philip S. Harrington. All
rights reserved. No
reproduction, in whole or in part, beyond single copies for use by an
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